Dosage forms manufactured in the shape of an osmotic device for delivering a drug to a biological environment of use are known to the dispensing art in U.S. Pat. Nos. 3,845,770 and 3,916,899, both issued to inventors Theeuwes and Higuchi. The dosage form disclosed in these patents comprises a semipermeable wall that surrounds a compartment containing a drug. There is a passageway in the wall for delivering the drug from the dosage form. The dosage form releases the drug by fluid being imbibed through the semipermeable wall into the compartment at a rate determined by the permeability of the wall and the osmotic pressure gradient across the wall. This action produces a solution containing soluble drug that is dispensed through the passageway over time.
The dosage form described in the above patents is an outstanding invention and represents a pioneer advancement in the delivery art. In U.S. Pat. No. 4,062,228 patentee Theeuwes made an inventive improvement in this dosage form for delivering drugs that are hard to deliver, particularly drugs that are insoluble in aqueous fluids. The invention in this latter patent consists essentially in charging the dosage form with an effervescent couple consisting of an acidic component and a basic component. In operation, when the dosage form is in a fluid environment, the couple imbibes fluid into the system, thereby wetting the couple causing it to reach and produce an effervescent solution. The effervescent solution is dispensed through a passageway from the dosage form. The effervescent couple instantly reacts in the presence of the imbibed fluid and immediately delivers the drug from the dosage form.
The dosage form disclosed in U.S. Pat. No. 4,062,288 presented immediately above represents a major advancement for delivering hard to delivery drugs, but it lacks the means for governing the rate of gas production over a prolonged period of time for correspondingly delivering the drug over a prolonged period of time.
In the light of this discussion, it will be readily appreciated by those skilled in the subject dispensing art that a critical need exists for a means for governing the rate of gas production over time accompanied by delivering the drug over a similar period of time. It will further appreciated by those skilled in the art, that if a novel and useful dosage form is made available for delivering these drugs, such a dosage form would have a positive value and also represents a substantial contribution to the dispensing art.